1. Field of the Invention
This invention relates to a separator plate for a fuel cell stack, preferably an internally manifolded molten carbonate fuel cell stack. This invention also relates to subassemblies of an anode/current collector/separator plate/current collector/cathode therefore which upon assembly provide effective sealing between said fuel cell components. The subassemblies provide ease of assembly resulting in reduced labor costs and long-term stability while the separator plate design simplifies the design of the interacting fuel cell components, reduces the assembly time in constructing a fuel cell stack, improves sealing by using a rigid and increased sealing area, prevents electrode creeping, eliminates the "cookie cutter" effect, and eliminates the internal resistance within each cell.
Generally, fuel cell electrical output units are comprised of a stacked plurality of individual cells separated by inert or bi-polar electronically conductive ferrous metal separator plates. Individual cells are sandwiched together and secured into a single stacked unit to achieve desired fuel cell energy output. Each individual cell generally includes an anode and cathode electrode, a common electrolyte tile or matrix, and a fuel and oxidant gas source. Both fuel and oxidant gases are introduced through manifolds to their respective reactant chambers between the separator plate and the electrolyte tile or matrix. In order to ensure proper functioning of the fuel cell stack, seals between the various cell components are required to maintain separation of the fuel and oxidant gases and prevent and/or minimize gas leakage.
This invention provides fully internal manifolding of the fuel and oxidant gases to and from the individual cells of an assembled fuel cell stack in a manner, due principally to the design of the separator plate, which provides ease of assembly, long-term endurance, stability of fuel cell operation, and a reduced number of individual cell components, thereby eliminating fit up problems between the various cell components.
2. Description of Prior Art
Commercially viable molten carbonate fuel cell stacks may contain up to about 600 individual cells, each having a planar area in the order of at least eight square feet. In stacking such individual cells, separator plates separate the individual cells with fuel and oxidant each being introduced between a set of separator plates, the fuel being introduced between one face of a separator plate and the anode side of an electrolyte matrix and oxidant being introduced between the other face of the separator plate and the cathode side of a second electrolyte matrix. Due to the thermal gradients between cell assembly and cell operating conditions, differential thermal expansions, and the necessary strength of materials used for the manifolds, close tolerances and very difficult engineering problems are presented.
Various means of sealing in the environment of high temperature fuel cells are taught, for example, by U.S. Pat. No. 5,342,706, U.S. Pat. No. 5,077,148, U.S. Pat. No. 5,045,413, and U.S. Pat. No. 5,227,256, all of which teach an internally manifolded fuel cell stack design utilizing a wet seal approach to sealing of the fuel cell stack. All of the separator plates taught by these U.S. patents are multi-piece separator plates. Multi-piece separator plates are also taught by U.S. Pat. No. 5,338,621.
U.S. Pat. No. 5,384,208 teaches a cell structure for electrolyzer units and fuel cells comprising an electrolyte-permeable diaphragm, one metallic, electrolyte-permeable electrode respectively on either side of the diaphragm, an electrically conductive bi-polar cell partition respectively which bounds the cells, one electrically conductive structure respectively between the electrode and the cell partition which acts as an elastic spacer and current supply, and a frame construction which encloses the cell on the circumference side. The cell partitions are constructed of sheet metal and, if necessary, spacers. The cell partition is constructed as a simple flat impermeable sheet metal plate.
U.S. Pat. No. 5,273,837 teaches a thermal-shock-resistant fuel cell design comprising flat and corrugated ceramic sheets combined to form channeled structures, the sheets being provided as thin, flexible ceramics and being particularly effective when used as components of compliant electrolyte substructures incorporating the flexible ceramics with fuel cell electrodes and/or current conductors bonded thereto. And, finally, U.S. Pat. No. 5,084,364 teaches a separator plate for stacking molten carbonate fuel cells having openings for fuel inlet and fuel outlet and oxidant inlet and oxidant outlet, the gas passages through the separator plate having a spring characteristic as a result of choosing a suitable profile therefore and as a result of a frame-type spring which is disposed around the active cell assembly, which frame-type spring contains built-in components for conveying the process gases where the profile of the frame spring is matched to the spring characteristic of the gas passage.